CN110087856B

CN110087856B - Co-extrusion method for manufacturing composite rubber molding element for tire

Info

Publication number: CN110087856B
Application number: CN201780078319.8A
Authority: CN
Inventors: M·鲁比; C·贝萨克
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 2016-12-20
Filing date: 2017-10-31
Publication date: 2021-07-06
Anticipated expiration: 2037-10-31
Also published as: WO2018114105A1; FR3060436A1; US20200101655A1; EP3558627A1; CN110087856A; EP3558627B1

Abstract

The invention relates to a method for co-extruding rubber molding elements. The method comprises extruding and shaping various rubber materials of a coextruded profiled element in a given coextrusion width and coextrusion DL1 direction perpendicular to the transverse Plane (PT), said method comprising the following series of steps: a) discontinuously extruding the first material, b) discontinuously forming the first material in a first pass, c) discontinuously extruding the second material, d) forming the first material and the second material to form at least one longitudinal groove (26) in the forming element (20) and, at the same time, extruding at least a third material next to each longitudinal groove (26) formed in the forming element (20), e) finally forming the first, second and third materials to a final profile (P74), the final profile (P74) being free of discontinuities in the coextruded width (L50).

Description

Co-extrusion method for manufacturing composite rubber molding element for tire

Technical Field

The present invention belongs to the field of tyre manufacture, more precisely to the field of co-extrusion (co-extrusion) of composite rubber profiled elements.

Background

By a composite rubber profiled element is meant a profiled element consisting of different profiled elements which are made of different elastomer compounds and which are assembled to one another.

When manufacturing green tires, the form of the profiled element of the tire tread placed on the profiled carcass takes the form of a portion cut from a composite and unvulcanized rubber profiled element.

More specifically, as shown in FIG. 1, the portion of the composite rubber profiled element 10 includes a laterally continuous base layer 12 with another laterally continuous layer 14 overlying the base layer 12. This other layer 14 is called tread, since the layer 14 is intended to be brought into contact with the ground when the tire is running along the ground. Because the base layer 12 is not intended to be in contact with the ground, it is made of a different elastomeric compound than the tread 14 and does not have, for example, the same composition or the same properties and performances.

The composite rubber profiled element is obtained by coextrusion according to known manufacturing methods. Using this technique, the various profiled elements of different compounds of the composite profiled element are extruded and assembled simultaneously on a single manufacturing machine.

The coextrusion also allows to manufacture composite shaped elements, comprising the underlayer 12, the tread 14 and other protective shaped elements superimposed on the lateral ends of the tread 14 and made of a third elastomeric compound whose composition and characteristics are different from those of the underlayer compound and of the tread compound.

However, like the base layer 12 and the tread 14, these protective molding elements are laterally continuous.

Because of the poor electrical conductivity of the elastomeric compound used to make the base layer 12 and the tread 14, co-extruders have been developed that enable the co-extruded base layer 12 and tread 14 to have inserts through the base layer 12 and tread 14 that are made from the electrically conductive elastomeric compound.

Such a coextrusion machine is described, for example, in european patent EP 1448355.

According to this document EP1448355, the machine provides a main extruder having an extrusion head with at least two ducts for the flow of the underlayer and tread rubber compounds, said ducts leading to extrusion orifices through which the two (underlayer and tread) rubber compounds are discharged, said extrusion orifices being delimited by a first wall and a second wall.

In order to form the electrically conductive insert through the base layer and the tread of the co-extruded composite profiled element, the extrusion head further comprises at least one micro-extruder of the third (electrically conductive) rubber compound, and the extrusion head of the micro-extruder is equipped at its end with a nozzle passing through the two flow ducts so that the third (electrically conductive) rubber compound is inserted into the base layer and the tread rubber compound upstream of the extrusion orifice.

A first drawback is that the nozzle described in this document EP1448355 is not suitable for extruding inserts made of elastomeric compounds that impart an excellent stiffness, or at least a higher stiffness than the stiffness imparted by each of the underlayer and the tread by their respective compounds. This is because the extrusion pressure required for such compounds is too high compared to the extrusion pressure used for extruding the base and tread compounds, which may deteriorate the quality of the coextruded composite profiled element, in particular resulting in an extruded insert that is much wider than required for electrical conductivity, or the cross-section may vary randomly along the length of the profiled element.

Another disadvantage is that the nozzle does not allow the third material to be extruded with a precise cross-section in the transverse plane of the composite profiled element, whether or not the third compound extruded through the nozzle imparts high stiffness to the insert. Furthermore, the nozzle also does not form an insert whose two sides are not flanked by the tread and the under layer.

However, with the increasing use of treads made of elastomeric compounds which give these treads an increasingly lower stiffness and therefore an increasingly higher hysteresis, it is now necessary in the tyre manufacturing industry to reinforce composite tread-forming elements by means of inserts having a precise cross section in the transverse plane of the composite forming element, not flanked by the tread and by the underlayer, and made of elastomeric compounds which give the inserts a stiffness higher than that imparted by their respective compounds on the underlayer and on the tread.

Disclosure of Invention

It is therefore an object of the present invention to overcome at least one of the drawbacks identified in the prior art and to meet the above-mentioned industrial needs.

To this end, one subject of the invention is a coextrusion process for manufacturing a composite rubber profiled element for tyres, said composite profiled element comprising, along its height, a first layer of a first rubber material, called underlayer, and a second layer of a second rubber material, called tread, said second layer being superimposed on said underlayer, the tread and the underlayer having at least one discontinuity over the width of the composite profiled element extending in the transverse direction, so that at least one insert of a third rubber material is inserted in the discontinuity of the tread and of the underlayer upon coextrusion.

According to the invention, the method comprises extruding and shaping various rubber materials in a given coextrusion width and coextrusion DL1 direction perpendicular to the transverse plane of the coextruded shaped element, said method comprising the following series of steps:

a) the first material is extruded discontinuously over the width of the coextrusion,

b) the first material is shaped discontinuously over the coextrusion width,

c) discontinuously extruding a second material across the coextruded width and superposing the second material on the first material,

d) shaping the first material and the second material into a profile without discontinuities in the coextruded width but forming at least one longitudinal groove in the shaping element, the shaping being carried out jointly with at least one extrusion of the third material next to each longitudinal groove formed in the shaping element,

e) the first, second and third materials are finally shaped into a final profile without discontinuities in the coextruded width, but such that its final shape is able to impart to each longitudinal groove formed in the shaped element in the preceding step d) and laterally alongside each insert resulting from the extrusion of the third material according to the preceding step d).

Drawings

Other features and advantages of the present invention will become apparent from the following description. This description, given by way of non-limiting example, refers to the accompanying drawings, in which:

FIG. 1 is a schematic view of a cross section of a composite rubber profiled element according to the prior art,

FIG. 2 is a schematic illustration of a cross-section of a composite rubber profiled element, which can be produced with a co-extrusion head according to the invention,

FIG. 3 is a schematic side view of a co-extruder comprising a co-extrusion head according to the invention,

FIG. 4 is a perspective view of a coextrusion head according to the invention;

FIG. 5 is a detailed front view of a coextrusion head according to the invention;

FIG. 6 is a first view of a longitudinal section of a coextrusion head according to the invention;

FIG. 7 is a second view of a longitudinal section of a coextrusion head according to the invention;

FIG. 8 is a third view of a longitudinal section of a coextrusion head according to the invention;

fig. 9 is a fourth view of a longitudinal section of a coextrusion head according to the invention.

Detailed Description

Fig. 2 schematically illustrates a composite rubber molding element for manufacturing a tire and which can be manufactured by using the co-extrusion method of the present invention.

The composite rubber molding element 20 includes, along its height H20, a first layer 22 of a first rubber material (which is referred to as the base layer), and a second layer 24 of a second rubber material (which is referred to as the tread) superposed on the base layer 22.

By rubber material is meant an unvulcanized elastomeric compound. In the context of the present invention, the base layer 22 and the tread 24 are made of different materials and therefore of elastomeric compounds that do not have the same composition and/or the same characteristics.

In addition, to create circumferential voids for future tires, the composite rubber profiled element 20 also includes longitudinal grooves 26. In the example shown in fig. 2, the composite rubber profiled element 20 has three longitudinal grooves 26. The three longitudinal grooves 26 extend parallel to each other in a DL direction taken along the length of the composite profiled element 20. The three longitudinal grooves 26 are spaced apart from one another in a transverse direction DT taken across the width W20 of the composite profiled element 20. The three longitudinal grooves 26 extend depthwise into the height H20 of the composite profiled element 20 without passing through the composite profiled element 20. These three longitudinal grooves 26 open onto the upper surface S24 of the tread 24. These three longitudinal grooves 26 divide the forming element into four longitudinal blocks 30, in which blocks 30 the tread pattern of the future tire will be molded. The two central blocks 30 have a substantially parallelepiped contour in the transverse plane PT of the composite profiled element 20, while the end blocks 30 have a substantially trapezoidal contour in the transverse plane PT of the composite profiled element 20 and taper towards the transverse ends 32 in the transverse direction DT of the composite profiled element 20.

According to the invention, the tread 24 and the underlayer 20 have at least one discontinuity D20 in the width W20 of the composite profiled element 20, so that at least one insert 28 of a third rubber material is inserted in each discontinuity D20 of the tread 24 and the underlayer 22 during co-extrusion.

Since the composite rubber molding element 20 has three longitudinal grooves 26 in the example shown in fig. 2, the tread 24 and the underlayer 22 present three discontinuities D20 in the width W20 of the composite molding element 20 and at least one insert 28 in each of these discontinuities D20.

The third rubber material from which the insert 28 is made is different from the material of the base layer 22 and the tread 24. The third material of the insert 28 is an elastomeric compound having a different composition and/or different properties than the compound forming the base layer and the tread. Advantageously, the third material of the insert 28 provides a higher stiffness than the materials of the base layer 22 and the tread 24. Accordingly, the inserts 28 may be able to reinforce the longitudinal blocks 30, thereby allowing the use of less rigid materials for the formation of the tread 24 and providing better traction for future tires.

More specifically, each insert 28 extends into the height H20 of the composite profiled element 20 without passing through the composite profiled element 20, and the thickness of the bottom layer 22 is present below each insert 28. Each insert 28 has a precise cross-section in the transverse plane PT of the profiled element 20. Thus, the cross-section of the insert 28 in the transverse plane PT comprises at least one triangular sub-portion.

According to the invention, the cross-section of the insert 28 in the transverse plane PT is triangular. In addition, two inserts 28 of triangular cross-section may be located in the same discontinuity D20, while being separated from each other in the transverse direction DT. The bottom of the longitudinal groove 26, whether or not one or two inserts 28 are present in the discontinuity D20, is constituted by a strip 38 of substantially parallelepiped cross-section of the material of the tread 24.

Each insert 28 forms a side wall 34 of the block 30. Thus, a first face F1 of the insert 28 extending along the height H20 of the molding element 20 is closely adjacent to the material of the tread 24, a second face F2 of the insert 28 extending into the height H20 of the molding element 20 forms the sidewall 34 of the block 30, and a third face F3 of the insert 28 is closely adjacent to the material of the underlayer 22.

To co-extrude the composite profiled element 20, the present invention proposes a co-extrusion head 50. As shown in fig. 3, head 50 is adapted to be mounted on a co-extruder 52 having a cylindrical roller 54. To this end, the head 50 has a lower wall 56 of cylindrical profile, said lower wall 56 extending longitudinally with a constant radius in the DL1 direction of the tread around a central axis AC1 and transversely in a straight line in a transverse direction DT1 parallel to the central axis AC1 and perpendicular to the DL1 direction. The lower wall 56 is adapted to be attached to an outer wall 58 of the cylindrical roller 54 so that the composite profiled element 20 can be coextruded. During operation of the coextruder, cylindrical roller 54 rotates R1 about central axis AC 1.

According to the invention, from upstream to downstream of this lower wall 56 of cylindrical profile, and in the direction of DL1, the head 50 comprises:

a) a first extrusion unit B60, comprising a first extrusion duct 60, said first extrusion duct 60 opening into the lower wall 56 of the coextrusion head, which first extrusion duct 60 is divided in the transverse direction DT1 into individual sub-ducts 60-1, 60-2, 60-3, 60-4,

b) a first forming blade 62, which defines intermittently in the transverse direction DT1 a first forming profile P62, which first forming profile P62 is discontinuous in the transverse direction DT1 and is located radially outside the lower wall 56 of the co-extrusion head,

c) a second extrusion unit B64, comprising a second extrusion duct 64, said second extrusion duct 64 opening out to the lower wall 56 of the coextrusion head, which second extrusion duct 64 divides in the transverse direction DT1 into individual sub-ducts 64-1, 64-2, 64-3, 64-4,

d) a second forming blade 66 defining a second forming profile P66, said second forming profile P66 being located radially outside the lower wall 56 of the co-extrusion head, this second profile P66 being free of discontinuities in the transverse direction DT1, but the second forming blade 66 having at least one tooth 67-1, 67-2, 67-3 extending radially inwards but not reaching the lower wall 56 of the co-extrusion head, each tooth 67-1, 67-2, 67-3 being located in a continuation of the divider 72-1, 72-2, 72-3 in the direction DL1, said divider 72-1, 72-2, 72-3 dividing the first extrusion duct 60 into sub-ducts 60-1, 60-2, 60-3, 60-4 in the transverse direction DT1, discontinuities being formed in the first forming profile P62 of the first forming blade 62 in the transverse direction DT1, and divides the second extruded tube 64 into sub-tubes 64-1, 64-2, 64-3, 64-4 in the transverse direction DT1, and the second forming blade P66 includes: at least one third extrusion conduit 68-1, 68-2, 68-3 opening into the lower wall 56 of the coextrusion head, each outlet 70-1, 70-2, 70-3, 70-4 of the third extrusion conduit closely abutting a tooth 67-1, 67-2, 67-3 of the second forming blade 66, and

e) a third forming blade 74 defining a final forming profile P74, said final forming profile P74 being located radially outside the lower wall 56 of the co-extrusion head, the final forming profile P74 being free of discontinuities in the transverse direction DT1, the third forming blade 74 having at least one tooth 74-1, 74-2, 74-3 extending radially inwardly but short of the lower wall 56 of the co-extrusion head, each tooth 74-1, 74-2, 74-3 of the third forming blade 74 being located in front of a tooth 67-1, 67-2, 67-3 of the second forming blade 66.

While first extrusion conduit 60 allows the first material of bottom layer 22 to be extruded, sub-conduits 60-1, 60-2, 60-3, 60-4 allow the first material to be discontinuously extruded in a coextrusion width L50 of coextrusion head 50. Thus, the subducts 60-1, 60-2, 60-3, 60-4 may create a discontinuity D20 in the bottom layer 22 upon extrusion of the first material.

Next, the discontinuous first forming blade 62 includes the projecting shapes 62-1, 62-2, 62-3, the projecting shapes 62-1, 62-2, 62-3 extending radially inward up to the lower wall 56 and enabling the formation of the first material of the sub-layer 22 while maintaining the discontinuity D20 created upstream in the sub-layer by the sub-conduits 60-1, 60-2, 60-3, 60-4.

While second extrusion conduit 64 allows the second material of tread 24 to be extruded, sub-conduits 64-1, 64-2, 64-3, 64-4 allow the second material to be discontinuously extruded in a coextrusion width L50 of coextrusion head 50. Thus, once the second material is extruded, the subducts 64-1, 64-2, 64-3, 64-4 may create a discontinuity D20 in the tread 24.

The teeth 67-1, 67-2, 67-3 of the second forming blade 66 then enable the first and second materials of the underlayer 22 and of the tread 24 to be formed in continuation of the discontinuity D20, said discontinuity D20 being produced upstream in the underlayer 22 and in the tread 24 by the sub-ducts 60-1, 60-2, 60-3, 60-4 of the first duct 60 and the sub-ducts 64-1, 64-2, 64-3, 64-4 of the second duct 64.

By closely abutting the teeth 67-1, 67-2, 67-3 of the second forming blade 66, the outlets 70-1, 70-2, 70-3 of each third extrusion conduit 68-1, 68-2, 68-3 allow the third material to be extruded in the region of the sidewall 34 of the future channel 26 and thus enable an insert 28 of this third material to be formed in the forming element 20.

The third forming blade 74 completes the formation of the three materials and provides the desired final exit profile for the forming element 20. Each tooth 74-1, 74-2, 74-3 of this third blade 74 is located in the continuation of the tooth 67-1, 67-2, 67-3 of the second forming blade 66 and enables a groove 26 to be formed in the composite forming element 20, which groove 26 closely adjoins one or both inserts 28 in the transverse direction DT 1.

In co-extrusion head 50 according to the present invention, each of the protruding shapes 62-1, 62-2, 62-3 of first forming blade 62 forms a portion of divider 72-1, 72-2, 72-3, respectively.

When co-extrusion head 50 is mounted on co-extruder 52,

tubes

60, 64 and sub-tubes 60-1, 60-2, 60-3, 60-4, 64-1, 64-2, 64-3, 64-4 open into lower wall 56, and the forming profiles P62 and P66 of the first and second forming blades are closed by outer wall 58 of roll 54.

To form the non-zero height and width strip 37 from the first material under each insert 28 of the bottom layer 22, each divider 72-1, 72-2, 72-3 includes at least one longitudinal slit 94-1, 94-2, 94-3, 94-4, the longitudinal slits 94-1, 94-2, 94-3, 94-4 extending from the first extrusion unit B60 to the second extrusion unit B64 via the first forming blade 62 and extending radially outward in a height direction from the lower wall 56 of the co-extrusion head.

Considering the longitudinal surfaces 96-1, 96-2, 96-3, 96-4 of each partition 72-1, 72-2, 72-3 facing the first extrusion unit B60 and the first forming blade 62 and the second extrusion unit B64, extend in a radial direction at a respective constant height from the lower wall 56 of the coextrusion head, starting from the longitudinal cut.

More specifically, as shown in FIG. 7, longitudinal surfaces 96-1, 96-2, 96-3, 96-4 of the longitudinal slits, when belonging to first extrusion unit B60, extend at a first height H1 with respect to lower wall 56 of the co-extrusion head; the longitudinal surfaces 96-1, 96-2, 96-3, 96-4 of the longitudinal cut, when belonging to the first forming blade 62 and to the second extrusion unit B64, extend with a second height H2 with respect to the lower wall 56 of the coextrusion head, the first height H1 of the longitudinal surfaces being greater than the second height H2 of the longitudinal surfaces. Thus, the height of the first material present in the longitudinal cut gradually decreases in steps, so that the correct geometry of the strip 38 below the insert 28 of first material can be ensured.

In order to extrude a strip 37 of first material of non-zero height and width upstream of each third material outlet portion, each longitudinal slit 94-1, 94-2, 94-3, 94-4 opens upstream and faces an outlet 70-1, 70-2, 70-3, 70-4 of a third extrusion conduit 68-1, 68-2, 68-3 of the second forming blade P66.

Furthermore, when the longitudinal surface belongs to the first forming blade 62 and to the second extrusion unit B64, the longitudinal surface 96-1, 96-2, 96-3, 96-4 of the longitudinal slit extends with a height H2 with respect to the lower wall 56 of the co-extrusion head, and the lower edge 71-1, 71-2, 71-3, 71-4 of each outlet 70-1, 70-2, 70-3, 70-4 of the third extrusion duct 68-1, 68-2, 68-3, 96-4, which is open with the longitudinal surface 96-1, 96-2, 96-3, 96-4 facing, extends with a height H3 with respect to the lower wall 56 of the co-extrusion head, the lower edge 71-1, 71-2, 71-3, 71-4 of the outlet 70-1, 70-2, 70-3, 70-4, 71-3, 71-4 is greater than the height H3 of the longitudinal surfaces 96-1, 96-2, 96-3, 96-4 belonging to the first forming blade 62 and the second extrusion unit B64, H2.

In order for the cross-section of the insert 28 to have at least one triangular sub-portion in the transverse plane PT of the profiled element 20, the outlet cross-section of each third duct 68-1, 68-2, 68-3 comprises: at least one triangular sub-portion in a transverse plane PT50 perpendicular to the direction of DL 1. More specifically, one vertex of the triangular sub-portion extends radially outward from the lower wall 56 of the co-extrusion head.

To form two triangular inserts 28 on either side of the channel 26 of the forming element 20, the third extrusion conduit 68-1 includes: two outlets 70-1, 70-2, the outlets 70-1, 70-2 being closely adjacent either side of the teeth 67-1 of the second forming blade P66, each of these outlets 70-1, 70-2 having a triangular cross-section.

Moreover, the divider 72-1, located upstream of the tooth 67-1 (which flanks the two outlets 70-1, 70-2 of the third extrusion conduit 68-1), comprises two transverse longitudinal cuts 94-1, 94-2, each of these transverse longitudinal cuts 94-1, 94-2 facing one of the two outlets 70-1, 70-2 of the third extrusion conduit 68-1.

In order to extrude the strip 38 of the tread 24 forming the bottom of the groove 26 surrounded by two inserts 28 of triangular cross-section, each partition 72-1 (provided in its continuation with a tooth 67-1 closely adjacent to the two outlets 70-1, 70-2) has an internal duct 76, the inner conduit 76 connects at least one sub-conduit 64-1, 64-2 of the second extrusion conduit 64 to the lower wall 56 of the co-extrusion head, preferably connects two sub-conduits 64-1, 64-2 of the second extrusion conduit 64 to the lower wall 56 of the co-extrusion head, the inner conduit 76 opens to the lower wall 56 upstream of the two outlets 70-1, 70-2 of the third conduit 68-1 in the direction DL1 and opens between the two outlets 70-1, 70-2 in the transverse direction DT 1.

As shown in FIG. 4, this inner conduit 76 is created by a divider 72-1, the divider 72-1 dividing the second extrusion conduit 64 into two subducts 64-1, 64-2, and two triangular outlets 70-1, 70-2 of a third duct 68-1 at a distance are provided in the continuation of the divider 72-1. Preferably, to ensure that the inner conduit 76 is supplied with tread material 24, the inner conduit 76 includes two inlets 78-1, 78-2 connected to the two sub-conduits 64-1, 64-2, respectively.

In the example shown in the figures, co-extrusion head 50 includes three dividers 72-1, 72-2, 72-3 in transverse direction DT1 that divide first extrusion conduit 60 into four sub-conduits 60-1, 60-2, 60-3, 60-4, create three discontinuities in first forming profile P62 of first forming blade 62, and divide second extrusion conduit 64 into four sub-conduits 64-1, 64-2, 64-3, 64-4. The protruding shapes 62-1, 62-2, 62-3 of the first forming blade 62 form an integral part of these spacers 72-1, 72-2, 72-3.

Still in the example shown in the figures, co-extrusion head 50 comprises, in transverse direction DT1, two consecutive partitions 72-3, 72-2, each followed by a single triangular outlet 70-4, 70-3 in the DL1 direction, while the first partition 72-1 is followed by two triangular outlets 70-1, 70-2 in the DL1 direction.

To extrude the various materials of the tread 24, base layer 22, and insert 28, and as shown in fig. 3 and 6, the first conduit 60 is connected to a first extruder E60, the second conduit 64 is connected to a second extruder E64, and the third conduit 68-1, 68-2, 68-3 of the second forming blade 66 is connected to a third extruder E68.

More specifically, third conduits 68-1, 68-2, 68-3 of second forming blade 66 are connected to third extruder E68 via

conduits

84, 86, which

conduits

84, 86 lead to an upper surface 88 of co-extrusion head 50.

As shown in fig. 7, first extrusion conduit 60 belongs to first extrusion unit B60, and first extrusion conduit 60 leads to rear surface 90 of co-extrusion head 50, where it is connected to first extruder E60. Second extrusion conduit 64 belongs to second extrusion unit B64, and second extrusion conduit 64 leads to rear surface 90 of co-extrusion head 50, where it is connected to second extruder E64.

As shown in fig. 6 to 9, the third pipes 68-1, 68-2, 68-3 of the second forming blade 66 are formed in the main body 92 of the second forming blade 66, and the

pipes

84, 86 connecting them to the third extruder E68 are formed through the second extrusion unit B64.

Also, the co-extrusion head 50 is formed by assembling the first extrusion unit B60, the first forming blade 62, the second extrusion unit B64, and the second and third forming

blades

66 and 74.

More generally, the invention also relates to a method of co-extruding a composite rubber molding element 20 for manufacturing a tire, which can be carried out in particular using the co-extrusion head 50 previously described.

According to the invention, the method comprises extruding and shaping the various rubber materials of the profiled element 20 in a co-extruded DL1 direction of a given co-extrusion width L50 and perpendicular to the transverse plane PT of the co-extruded profiled element, said method comprising the following series of steps:

a) the first material is discontinuously extruded over the coextruded width L50,

b) the first material is discontinuously formed over the coextruded width L50,

c) the second material was discontinuously extruded over the coextruded width L50, and was superposed on the first material,

d) shaping the first and second materials according to a profile P66, said profile P66 having no discontinuities over the coextrusion width L50 but forming at least one longitudinal groove 26 in the shaping element 20, the shaping being carried out jointly with at least one extrusion of the third material alongside each longitudinal groove 26 formed in the shaping element 20,

e) the final shaping of the first, second and third material takes place according to a final profile P74, this final profile P74 being free of discontinuities over the coextruded width L50, but such that its final shape is able to impart to each longitudinal groove 26 formed in the shaped element 20 in the preceding step d) and laterally alongside each insert 28, said insert 28 resulting from the extrusion of the third material according to the preceding step d).

Advantageously, by extruding the third material of the insert 28 at the end of the co-extrusion process, the geometry of the extruded insert 28 is preserved from the flow of the upstream extruded first and second materials.

More specifically, because the third material is extruded alongside each longitudinal groove 26 according to a shaped outlet cross-section, a strip of non-zero height and width of the first material is extruded upstream of and below each third material outlet portion.

More specifically, in order to ensure the correct geometry of the strip 38 of first material present under the insert 28, the height of the first material extruded upstream of each third material outlet portion is progressively reduced.

More specifically, the height of the first material extruded upstream of each third material outlet portion is reduced in stages.

During step d), the third material is extruded according to an outlet cross section comprising at least one triangular sub-portion in the transverse plane PT50, and such that the triangular sub-portion constitutes one side wall of the longitudinal groove 26 formed in the forming element 20.

In order to form two triangular inserts 28 on either side of the groove 26 of the profiled element 20, during step d), a third material is extruded according to an outlet cross-section containing, in the transverse plane PT50, two triangular sub-portions that are distant from each other in the transverse direction DT1 of extrusion, and such that the third material extruded by these triangular sub-portions constitutes the two side walls of the longitudinal groove 26 formed in the profiled element 20.

In order to extrude the strip 38 of tread 24 forming the bottom of the groove 26 surrounded by two inserts 28 of triangular cross-section while performing step c), the flow portion of the second material is diverted towards a discontinuity D20 formed during steps a), b) and c) in the first and second material superposed and such that the diverted flow of the second material reaches between two triangular outlet sub-portions of the third material in the transverse direction DT1 of the extrusion.

To insert the insert 28 into the three longitudinal grooves 26 of the profiled element 20, during steps a) to d), three discontinuities are formed in the first material and in the second material in the transverse direction DT1 of the extrusion.

If the process is carried out on a co-extruder 52 with rolls 54, the co-extruded DL1 direction extends with a constant radius around the central axis AC 1.

Preferably, the extrusion and forming steps of the method are performed between a roller 54 and an extrusion head 50, the extrusion head 50 comprising a lower wall 56 of cylindrical profile cooperating with an outer wall 58 of the roller.

The invention also relates to a composite rubber profiled element obtained by the method described previously (and for example using the co-extrusion head described previously).

At the same time, the invention also covers a tyre made from a composite rubber profiled element obtained according to the method described previously.

Claims

1. A co-extrusion method for manufacturing a composite rubber profiled element (20) for a tyre, the profiled element (20) comprising, along its height (H20), a first layer (22) of a first rubber material and a second layer (24) of a second rubber material, the first layer (22) being called a base layer and the second layer (24) being called a tread, the second layer (24) being superimposed on the base layer, the tread (24) and the base layer (22) having, over a width (W20) of the profiled element extending along a transverse Direction (DT), at least one discontinuity (D20) such that at least one insert (28) of a third rubber material is inserted into the discontinuities (D20) of the tread (24) and base layer (22) upon co-extrusion, the third rubber material of the insert (28) providing a higher stiffness than the first rubber material of the base layer (22) and the second rubber material of the tread (24), the method comprises the following steps: extruding and shaping various rubber materials in a given coextruded width (L50) and coextruded DL1 direction perpendicular to the transverse Plane (PT) of the coextruded shaping element, the method comprising the series of steps of:

a) discontinuously extruding the first material across the coextruded width (L50),

b) the first material is formed discontinuously over the coextrusion width (L50) in a first pass,

c) discontinuously extruding a second material across the coextruded width (L50), and superposing the second material on the first material,

d) shaping the first and second materials into a profile (P66), said profile (P66) being free of discontinuities over the coextrusion width (L50) but forming at least one longitudinal groove (26) in the shaping element (20), the shaping being carried out jointly with at least one extrusion of the third material alongside each longitudinal groove (26) formed in the shaping element (20),

e) -final shaping of the first, second and third material into a final profile (P74), said final profile (P74) being free of discontinuities over the coextruded width (L50), but such that its final shape is able to impart to each longitudinal groove (26) formed in the shaped element (20) in the preceding step d) and laterally alongside each insert (28), said insert (28) resulting from the extrusion of the third material according to the preceding step d);

wherein a third material is extruded alongside each longitudinal groove (26) according to a shaped outlet cross-section, a strip of non-zero height and width of the first material being extruded upstream of and below each third material outlet portion.

2. Method for co-extrusion of a composite rubber profiled element (20) according to claim 1, wherein the height of the first material extruded upstream of each third material outlet portion is gradually reduced.

3. Method for co-extrusion of a composite rubber profiled element (20) according to claim 2, wherein the height of the first material extruded upstream of each third material outlet portion decreases in stages.

4. Method for co-extrusion of a composite rubber profiled element (20) according to any one of the preceding claims, wherein during step d) the third material is extruded according to an outlet cross-section comprising at least one triangular sub-portion in the transverse plane (PT50) and such that the triangular sub-portion constitutes one side wall of a longitudinal groove (26) formed in the profiled element (20).

5. Method for co-extrusion of a composite rubber profiled element (20) according to claim 4, wherein during step d) the third material is extruded according to an outlet cross section containing in a transverse plane (PT50) two triangular sub-sections distant from each other in the transverse direction (DT1) of extrusion, and such that the third material extruded by these triangular sub-sections constitutes the two side walls of the longitudinal groove (26) formed in the profiled element (20).

6. Method for co-extrusion of a composite rubber profiled element (20) according to claim 5, wherein, while performing step c), the flow portion of the second material is diverted towards a discontinuity (D20), said discontinuity (D20) being formed in the superposed first and second materials during steps a), b) and c), and such that the diverted flow of the second material reaches between two triangular sub-portion outlets of the third material in the transverse direction of extrusion (DT 1).

7. Method of co-extrusion of a composite rubber profiled element (20) according to claim 1, wherein during steps a) to c) three discontinuities (D20) are formed in the first and second material in the transverse direction of extrusion (DT 1).

8. Method for co-extrusion of a composite rubber profiled element (20) according to claim 1, wherein the co-extruded DL1 direction extends with a constant radius around the central axis (AC 1).

9. Method for co-extrusion of a composite rubber profiled element (20) according to claim 1, wherein the extrusion and profiling steps are carried out between a roller (54) and an extrusion head (50), the extrusion head (50) comprising a lower wall (56) of cylindrical profile cooperating with an outer wall (58) of the roller.

10. A composite rubber profiled element (20) obtained by a method according to one of the preceding claims.

11. A tyre made from a composite rubber profiled element (20) according to claim 10.